Rikimaru is a swordsman in search of vengeance. Someone who was dear to him was killed by someone and he is looking for the killer. However, he ran out of money and ended up starving at Ryube. He was helped by Riou and then joins Viktor's mercenaries to keep himself fed. He continued to serve in the Unification Army and was often seen at Hai Yo's restaurant. After the war, he returned to kaku. - Blue Moon

Gameplay Information for Suikoden II

How to Recruit: Speak with him in Ryube and agree to make the payment for his meal.
Alternate Method: Speak with him in Coronet after the destruction of Ryube and agree to make the payment for his meal (only if you missed him in Ryube).